You are allowed 23 players for the two games, I'm not sure how many players you expect to not even travel out here, but if it happens I can see maybe two, three at most. It sounds like you're expecting two totally different squads.
That is easily close to half a squad that maybe travels to NZ but does not need to play.
But you can't be sure your 14 or 15 man squad is enough. What happens if they come out here and two or three players get injured in training or the warm-up? Or it's 0-0 after 70 minutes and the coach thinks "I really wish we had Messi or Higuain to bust this game open"?
EDIT: I think Messi would travel at least. He might not play or only come off the bench, but I don't think they'll be as precious with his as to have him stay in Spain or Argentina.